As the winter approached a new trouble appeared. The brief enlistment terms of many of the men were expiring, and, wearied and discouraged, without proper food or clothing, these men withdrew from the army, and the regiments rapidly decreased in numbers. Recruiting and re-enlisting in the face of such conditions became almost impossible; yet Washington's steady persistence, his letters to Congress, his masterly hold on the siege of the British in Boston, his appeals for men and ammunition, were actually successful. His army was kept up by new and renewed material. Privateers, sent out by him upon the sea, secured valuable supplies. Henry Knox, a Boston bookseller, whom he had made colonel of artillery and despatched to New York and Ticonderoga, returned to the camps with heavy cannon and ammunition. The right wing of the American army was stationed at Roxbury, under General Artemas Ward, and the left wing, under Major-General Charles Lee and Brigadier-Generals Greene and Sullivan, at Prospect Hill. The headquarters of Washington were in the centre, at Cambridge, with Generals Putnam and Heath. Lee was not allied with the great Virginia family of that name. He was an Englishman by birth, somewhat of a military adventurer. Conceited, vain, and disobedient, he afterwards came near wrecking the cause which he had ambitiously embraced. Ward was a native of Massachusetts, a worthy man, but not distinguished for military capacity. Putnam was a gallant hero, taken from the plough, but more fitted to head small expeditions than for patient labor in siege operations, or for commanding a great body of troops.